Rotor stabilizer



March 4, 1969 A. LENKEY ETAL ROTOR STAB ILI ZER Filed June 8, 1967 Sheetof4 JAMES B. GRAESER JR. BY ANDREW LENKEY ATTORNEY M r 4. 1969 A. LENKEYI ETAL Q 3,430,852

ROTOR STABILIZER Filed June a, 19s? Sheet 2 of 4.

\ 1N/VEN'IORS:

22 JAMES B. GRAESER JR.

BY ANDREW LENKEY ATTORNEY March 4, 1969 A. LENKEY ETAL ROTOR STABILIZERSheet Filed June 8, 1967 FIG. 2 a

INVENTORSI JAMES B. GRAESER JR. ANDREW LENKEY ATTORNEY March 4, 1969 A.LENKEY ETAL 3,430,852

' ROTOR STABILIZER Filed June a, 1967 Sheet 4 of 4 (\1 i so s4 FIG. 3

FIG. 30.

INVENTORS BY ANDREW LENKEY ATTORNEY United States Patent 9 ClaimsABSTRACT OF THE DISCLOSURE Apparatus for stabilizing a spinning rotorbelow a predetermined speed of rotation which apparatus is completelyremovable from the centrifuge and in which a tractive electromagnetactuates a stabilizing member into engagement with the rotor below saidspeed.

Cross-references to related applications Copending application Ser. No.273,166, filed Apr. 15, 1963, now Patent No. 3,322,338 entitledCentrifuge Stabilizing Assembly With Heat Probe and assigned to theassignee of the present invention, relates to the same general subjectmatter.

The present invention relates generally to rotor stabilizing apparatusand particularly to improved apparatus for stabilizing centrifuge rotorsbelow a predetermined speed.

In high speed centrifuges employing relatively heavy rotors mounted uponand driven by small diameter, flexible spindles, instability or wobblingof the rotor usually occurs below a certain speed. This wobbling action,if permitted a wide excursion, has various adverse effects among whichare the creation of high stresses and the remixing of sample componentsseparated during the high speed portion of the centrifuge run.

Apparatus for stabilizing centrifuge rotors during low speed operationare known in which a rotor-stabilizing member is automatically moved toengage the rotor and prevent wobbling when the rotor speed drops below apredetermined level. Actuation of the stabilizing member has beenaccomplished in various ways, as for example, by a solenoid. Theapparatus of the prior art, however, has proven deficient in a number ofWays. For example, they utilize complex structures limiting access tothe interior of the rotor chamber, tend to chatter during operationthereby creating an objectionable noise level (especially when energizedby an A.C. power supply) and provide no Way of limiting the force withwhich the stabilizing member engages the rotor. This lattercharacteristic not only results in excessive component wear but may havethe effect of disturbing and remixing the separated components orsediment as a consequence of the rotor being jarred during decelerationafter a run.

Accordingly, the overall object of the present invention is to providean improved apparatus for stabilizing centrifuge rotors so as toovercome the aforedescribed problems.

More specifically, it is an object of this invention to provide asimplified centrifuge rotor stabilizing apparatus, which is completelyremovable from the centrifuge to permit complete access to thecentrifuge chamber interior.

It is another object of the present invention to provide a centrifugerotor stabilizing assembly which is substantially chatter and noisefree.

Yet another object of this invention is to provide apparatus foractuating a centrifuge rotor stabilizing member in which the engagementforce of the stabilizing member is limited so as to reduce and minimizecomponent wear and jarring of the rotor.

With these and other objects in view, the present in- 3,439,852 PatentedMar. 4, 1969 vention will be clearly understood in connection with theaccompanying drawings in which:

FIG. 1 is a plan view of a portion of a centrifuge machine including arotor stabilizing assembly embodying the present invention;

FIG. 2 is an elevation View, in section, of the apparatus of FIG. 1taken along the plane 2-2 showing the rotor stabilizer in the retractedor rotor-released position;

FIG. 2a is an elevation view, in section, similar to FIG. 2 showing therotor stabilizer in the advanced or rotorengaging position; and

FIGS. 3 and 3a are elevation views, in section, of a portion of therotor stabilizing apparatus showing in greater detail the geometry andrelative positions of the components in the rotor-released androtor-engaging positions.

Referring to the drawings, the reference numeral 10 designates acentrifuge rotor mounted for rotation on a small diameter, relativelyflexible spindle 12. Mounted on the top of the rotor coaxiallytherewith, is a sleeve 14 which provides a convenient handle formanipulating the rotor. The lower end of the resilient spindle 12 isrotatably driven through suitable gearing by an electric motor (notshown) located beneath the rotor. The rotor 10 spins within a chamber 16defined by a cylindrical steel housing 18 which concurrently functionsas a guard should the rotor explode under the strain created by therelatively high rotational velocity at which it is operated. A liner 19is mounted inside the chamber 16 proximate the interior surface of thehousing 18. The chamber interior is refrigerated by means (not shown)including evaporator coils surrounding the liner which serves to controlthe chamber temperature.

A stabilizing assembly, designated generally by the refence numeral 20,is mounted across the open top of the chamber 16. The assembly 20, whichis removable as a unit, is supported with respect to the centrifugemachine frame by means of three brackets 22, 24 and 26 secured to thehousing 18.

The stabilizing assembly includes a generally triangle-shaped base orsupport plate 28 which extends across the chamber 16. Suitably fastenedto the plate 28 proximate the extremities of the wider end, are fixedsupport pins 31 and 32. The pins and 32 are adapted to be received bydetents 34 and 36 formed in the brackets 22 and 24, respectively. Ablock 38 is mounted at the small end of the plate 28 for carrying amovable support pin 40. The pin 40 has an enlarged, pointed end 42adapted to be received by detents 44 in the bracket 26. The block 38 isprovided with a stepped longitudinal bore 46 having a shoulder 48, theend 42 of the pin 40 being slidably'received in the bore 46. The pin 40is biased outwardly by means of a coil spring 50 compressed within thebore 46 between the shoulder 48 and the pin end 42. The inner end of thepin 40 is grooved to receive a snap ring 52 which limits the outwardmovement of the pin.

To permit the stabilizing assembly 20 to be adjustably positioned up ordown within the chamber 16 in order to accommodate rotors of variousheights, several vertically spaced detents are formed in each of thebrackets 22, 24

and 26. To position the assembly 20 at any selected level within thechamber 16, the fixed pins 30 and 32 are inserted in the detents 34 and36 at the appropriate level and pin 40 is manually retracted andinserted in the corresponding detent 44 in bracket 26. It will beappreciated that the insertion and removal of the assembly 20 is therebymade exceedingly simple and the operation can be performed with onehand.

The support plate 28 is provided with a circular opening for receiving astabilizer support assembly 62 which carries a stabilizing member 64 andan electromagnetic actuating device for advancing the member 64 intocontact with the sleeve 14 on the rotor 10. The assembly 62 is suspendedfrom the plate 28 by a support bracket 66 which extends across theopening 60. The bracket 66 has a centrally located hole 68 having avertical axis positioned substantially coincident with the geometric orfigure axis of the rotor and spindle 12.

The following description relates to the stationary portion of theassembly 62. A fixed, outer housing 70 made of a suitablenon-magnetizable material such as aluminum and having an upright,cylindrical flange 72 projecting upwardly through the hole 68, is heldin place and suspended from the bracket 66 by means of a retaining ring74 mounted in a groove formed in the flange 72. The outer housing 70further has a depending flange portion 76 provided with an annular step78. Mounted within the step 78 is a circular plate 80 made of a suitablymagnetizable material. The plate 80 has a central, upwardly extendingannular lip 82 provided with a bore 84 coaxial with the cylindricalflange 72. The lip 82 functions as an electromagnet pole piece as willbe described in greater detail later. The upper end of the pole piece 82i dished out or cut away to form an inwardly sloping or tapered surface86. A sleeve 88, made of a non-magnetic material such as brass, is pressfit within the bore 84. The sleeve 88 has an upper rim 90 projectingupwardly a short distance from the inner, lower edge of the taperedsurface 86. The rim 90 serves as a stop means as will be describedbelow. Another non-magnetizable sleeve 92, which may also be made ofbrass or the like, is press fit about the outer surface of the polepiece 82 and within the bore defined by the flange 72. Carried withinthe outer housing 70 and disposed about the sleeve 92 is a donut shapedelectromagnet 94. A pair of electrical leads 96 extend through anopening 98 in the housing 70 for connection with external circuitry forenergization of the electromagnet 94. A cylindrical radiation shield 100is suitably secured to the undersurface of the plate 80 by rivets 102,for example, for the purpose of minimizing radiant energy exchangebetween the stabilizer member 64 and assembly 62 on the one hand and thechamber 16 on the other.

The following is a description of the movable components, actuated bythe electromagnet 94, for advancing the stabilizing member 64 intocontact with the sleeve 14. Slidably mounted within the sleeve 92 is agenerally cylindrical magnetizable armature 104 having an annular stepor undercut 106 formed therein in the bottom portion. The downwardlyprojecting flange 108 defined thereby is provided with a beveled lowersurface 110, the slope of which is substantially the same as that of thetapered surface 86 of the pole piece 82. The use of tapered surfaces oncoacting magnetic elements such as the pole piece 82 and armature 104,is well known in the art for providing larger forces for a given amountof linear travel and for minimizing chatter and noise. A narrow,ringlike flat surface 112 is retained at the lower edge of the armature104 for making contact with the upper edge of the sleeve 88 when thearmature is advanced to the rotorengaging position. By inspection of thegeometry of the armature 104, it will be appreciated that the depth ofthe undercut 106 determines the surface area of the conical surface 110.

The upper portion of a tube 114, made of non-magnetic material such asbrass, is press fit within the bore of the armature 104. The lowerportion of the tube 114 slides freely within the sleeve 88. A bearingassembly exterior housing 116 is aifixed to the tube 114 so as to moveup and down therewith. Specifically the housing 116 has an uprightcylindrical portion 118 about which the tube 114 is press fit. Thehousing 116 further includes a lower, depending cylindrical flange 120which defines an interior well 122. The flange 120 carries a ring-like,interior bearing housing 124 having a generally T-shaped crosssectionwith an upper, horizontal leg 126 and a vertical 4 leg 127. The interiorhousing 124 is supported within the well 122 by means of a retainingring 128 and a washer 130 interposed between the ring 128 and thehorizontal leg 126 of the housing 124. The outer diameter of theinterior housing 124 is substantially less than the inside diameter ofthe well 122. In this way, the interior housing 124 is free to slide,within limits, transversely of the axis of rotation of the rotor 10. Theexterior housing 116 is made of a nonmagnetic material such as aluminumand the interior housing 124 is preferably fabricated of aselflubricating plastic material such as the acetal resin material soldunder the trademark Delrin manufactured by E. I. du Pont de Nemours &Company. This material is characterized by the radical [(OCH Thus, thehousing 124 moves within the well 122 with its upper surface infrictional engagement with the undersurface of the horizontal portion ofthe exterior housing 116.

The stabilizing member 64, also made of Delrin or other suitableself-lubricating plastic, is carried by the inner race of a ball-bearing142 and locked in place between a snap ring 144 and a shoulder 146formed in the exterior surface of the member 64. The outer race 148 ofthe bearing 142 is similarly carried within the vertical leg 127 of thehousing 124 and is held in place by a retaining ring 150.

The movable portion of the stabilizer assembly is biased to theretracted or rotor-released position by a helical coil spring 152compressed between the horizontal surface of the undercut 106 on thearmature 104 and the upper horizontal face of the pole piece 82. It willbe seen that in the advanced position of the stabilizer, as depicted inFIG. 2a, the lower surface of the stabilizing member 64 comes intocontact with the upper edge of the sleeve 14. To facilitate engagementof these elements should there be misalignment due to rotoreccentricity, the lower surface of the member 64 may be tapered orrounded as shown. The downward travel of the armature, and hence that ofthe stabilizing member64 is limited by the rim 90 of the sleeve 88 whicheventually will be engaged by the surface 112 on the armature. It shouldbe pointed out that since the motor and transmission of the centrifugemachine are shock-mounted, some downward, vertical displacement of therotor and spindle is possible. Thus, as the stabilizing member 64 ismoved into engagement with the sleeve 14, there may be some slightdownward movement of the rotor 10.

One aspect of the present invention which will now be described, tendsto limit the force with which the stabilizing member 64 engages thesleeve 14 thereby minimizing the jarring or disturbance of the rotor 10which might otherwise tend to remix the sediment within the samplecontainers carried by the rotor. Referring specifically to FIGS. 3 and3a, the former shows the armature in the retracted or rotor-releasedposition while the latter shows the armature at its limit of travel inthe other direction corresponding to the rotor-engaging position. Itwill be seen that because of the undercut 106 on the armature 104,substantially all lines of flux emanating from the face of the armatureintercept the face of the pole piece irrespective of the air gap betweenthe elements within the limits of travel of the armature. In otherwords, the cross-sectional area defined by the lines of magnetic fluxbetween the faces remains substantially constant throughout the entirerange of travel of the armature. It will also be appreciated that thepole piece may be undercut instead of the armature so that the polepiece will have the smaller surface area. As a further obviousalternative, the surfaces may be made to slope outwardly instead ofinwardly toward the axis of rotation as depicted in the drawings.

With the cross-sectional area of the magnetic lines of flux being heldsubstantially constant, the only remaining variable which will affectthe attractive force on the armature is the air gap between the armatureand the pole piece. By providing the stop means 90 to limit the downwardtravel of the armature, and thereby retain an air gap between theelements, the device may be operated within a range in which force isapproximately linearly related to distance between the armature and polepiece. The residual air gap which is provided by the stop means alsofunctions to prevent jamming of the elements due to inexact machiningand prevents residual magnetism from holding the elements together afterde-energization of the electromagnet.

Means serving to energize the electromagnet 94 below a predeterminedspeed of rotation of the rotor to advance the member 64 includes thecircuitry shown schematically in FIG. 2. A speed transducer 160 ismounted to detect the rotational speed of the spindle 12. Transducer 160feeds a signal to a speed control circuit 162 having an output coupledvia the connection 164 to appropriate contacts (not shown) within thedetent 44 on the bracket 26. Corresponding contacts (not shown) on thepin head 42 of pin 40 serve to complete the connection between the speedsensor 160 and the leads 96 through a connector plug 166. Where theoutput signal from the circuit 162 is A.C., a diode 168 may be includedto rectify the signal and provide the electromagnet with DC.

Operation of the foregoing apparatus is as follows:

With a selected rotor mounted upon the spindle 12 the stabilizingassembly 20 is brought down into the chamber 16 to an appropriate level.At the selected level, fixed pins 30 and 32 are inserted into thecorresponding detents in brackets 22 and 24, respectively, pin 40 ispushed into the bore 46 and the narrow end of the assembly 20 is loweredinto the chamber into position. The pin 40 is then permitted to enterthe appropriate detent 44 in the bracket 26. It will be noted that theassembly 20 is a completely self-contained, removable unit requiring noexternal wiring and when removed permits complete access into thechamber 16 for installation or removal of a rotor. Inasmuch as the rotoris not yet operating, the electromagnet 94 will be energized therebyattracting the armature 104 and moving it along with the exteriorhousing 116 downwardly until the stabilizing member 64 engages thesleeve 14. The rotor is now started. It should be noted that the elasticaxis on which the rotor rests is never quite straight and consequentlythe equilibrium positions of the rotor at rest and while spinning athigh speed are not identical. A transition of the equilibrium positionof the rotor therefore occurs, accompanied by wobbling, usually at lowerspeeds of several thousand revolutions per minute. The lateraldisplacement or wobbling of the rotor during the transition range isminimized by frictional damping provided by the stabilizing member 64and the interior housing 124 in cooperation with the exterior housing116. While the member 64 spins with the rotor 10 within the ball bearing142, it describes, along with the interior housing 124, an orbiting pathabout the common axis of the non-rotating components of the assembly 62.The limiting amount of lateral displacement of the combination of theinterior housing 124 and stabilizing member 64 is determined by theclearance between the periphery of the interior housing 124 and theinterior wall of the flange 120.

After the rotor 10 has passed through its transition speed and has begunto rotate steadily about an axis (which, of course, will vary with therotor and the particular sample loading), the speed control circuit 162deenergizes the electromagnet 94. The coil spring 152 moves the armatureupwardly to retract the stabilizing member 64. The rounded lower surfaceof the member 64 tends to coaxially align the member with the axis ofrotation of the rotor 10 established above the transition speed so thatthe member 64 will already be properly oriented when it is lowered onceagain for engagement with the sleeve 14.

Following completion of the centrifuge run, the rotor 10 is graduallydecelerated. As it approaches the transition speed at which wobblingmight be expected to occur, a signal from the speed sensor 160 causes anoutput signal to appear on the connecting line 164 to once againenergize the electromagnet 94. The armature 104 thereby moves downwardlyagainst the force of the helical spring 152 until contact is made by themember 64 against the sleeve 14, the travel of the armature 104 beinglimited by the rim 90.

It will be obvious to those skilled in the art that variousmodifications may be made to the specific exemplary embodiments of theinvention described. While particular embodiments have been discussed,it will be understood that the invention is not limited thereto and thatit is contemplated to cover in the appended claims any suchmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a centrifuge rotor stabilizer in which a stabilizing member and abearing assembly in which said member is rotatably mounted, are advancedfrom a rotor-released position to a rotor-engaging position below apredetermined rotor speed, the improvement in which a movable,magnetizable element is secured to said bearing assembly;

a stationary, magnetizable element is mounted proximate said movableelement and separated therefrom by an air gap for attracting saidmovable element when said stationary element is magnetically energizedso as to move said bearing assembly and the stabilizing member to saidrotor-engaging position;

an electromagnet surrounds said stationary element for magneticallyenergizing said stationary element when said rotor speed is below saidpredetermined level; and

resilient means is interposed between said movable and said stationaryelements urging said elements apart.

2. Apparatus as defined in claim 1 in which said movable and stationaryelements have opposing,

tapered, parallel faces, the face on one of said elements having asmaller area than the face on the other of said elements, thecross-sectional area defined by the lines of magnetic flux between saidfaces remaining substantially constant throughout the entire range oftravel of said movable element.

3. Apparatus as defined in claim 1 in which said movable and stationaryelements have opposing parallel sloping faces, the face of one of saidelements having a smaller area than the face of the other of saidelements, the geometric projection of the face of smaller area normal tosaid face falling on the face of the other element within the limits oftravel of the elements relative to one another.

4. Apparatus as defined in claim 1 in which a stop means is disposedbetween said elements for limiting the travel of said movable elementthereby leaving an air gap between said elements when said bearingassembly and stabilizing member are in said rotor-engaging position.

5. In an apparatus for stabilizing a centrifuge rotor about its axis ofrotation within a predetermined speed range, said apparatus including astabilizer member rotatably mounted within a bearing assembly and meansoperatively associated with said assembly for advancing the combinationof said assembly and said stabilizer member whereby said member isbrought into engagement with said rotor when said rotor speed fallswithin said predetermined speed range, the improvement in which saidadvancing means comprises a substantially cylindrical, stationary polepiece mounted coaxially of the geometric axis of said rotor;

an electromagnet disposed about said pole piece for magneticallyenergizing said piece when said rotor speed is within said predeterminedrange; and

a generally cylindrical armature connected to said bearing assembly andpositioned coaxially of said pole piece and proximate thereto so as tobe attracted by said pole piece upon energization thereof.

6. Apparatus as defined in claim in which said armature and said polepiece have opposed, sloping, substantially parallel faces; and

the outer cylindrical surface of said armature is undercut to reduce thearea of said sloping face of said armature, the depth of said undercutbeing such that substantially all magnetic lines of flux emanating fromsaid sloping armature face intercept said sloping face of said polepiece irrespective of the position of said armature Within its range oftravel.

7. Apparatus as defined in claim 6 which includes stop means secured tosaid pole piece and projecting therefrom to be engaged by said armatureto limit its range of travel and maintain an air gap between saidarmature and pole piece when said armature is in its most advancedposition.

8. Apparatus for stabilizing a centrifuge rotor about its axis ofrotation during low speed operation, said apparatus including astabilizer member movable between rotor engaging and rotor releasedpositions, said rotor being mounted for rotation within a chamberdefined by a cylindrical housing, said housing including a plurality ofbrackets having detents for receiving pins mounted on said apparatus forsupporting same, including a base plate for carrying a stabilizer membersupport assembly;

a pair of spaced, fixed support pins attached to one WILLIAM I. PRICE,Primary Examiner.

end of said base plate and adapted to be received by a correspondingpair of said brackets; and

a retractable, spring-biased support pin attached to the opposite end ofsaid base plate and adapted to be received by a third of said brackets,said apparatus being supported solely by said pins when in place in saidchamber.

9. Apparatus as defined in claim 8 in which said base plate supportselectromagnetic means for actuating said stabilizer member toward saidrotor for engagement therewith below a predetermined speed;

said apparatus including means responsive to the rotational speed ofsaid rotor for energizing said electromagnet below said prede-' terminedspeed; and

means interconnecting said electromagnet and said speed-responsive meansincluding contact means on said spring-biased pin and on said thirdbracket for completing the circuit to said electromagnet.

References Cited UNITED STATES PATENTS 7/1934 Krauss 210144 5/1967Stallman et a1 233-23 US. Cl. X.R.

